This invention relates to a magnetic tape cassette suitable for use for a video tape recorder, an audio tape recorder or the like, and more particularly to a magnetic tape cassette which is provided on the front side thereof with a dust cover for selectively covering a front portion of a casing of the cassette.
In general, a tape cassette which has been conventionally used for a video tape recorder, an audio tape recorder or the like includes a cassette casing which is formed at the front portion thereof with an opening to run the magnetic tape. The casette casing is provided at the front portion thereof with a dust cover for selectively covering the front opening of the casing, which dust cover comprises a front lid pivotally mounted on the casing and a rear lid pivotally mounted on the front lid so both lids can be operated in association with each other to enclose the magnetic tape therebetween. The front and rear lids are constantly forced by an elastic force, to thereby close an enclosing space for the magnetic tape when the cassette is not being used. This results in dust or the like being prevented from sticking to the magnetic tape during nonuse of the cassette. Also, this closing allows the front and rear lids to protect the front and rear surfaces of a magnetic tape by interposing the tape therebetween, to thereby prevent a user from contacting the magnetic tape by mistake during handling of the tape cassette, so that the magnetic tape may escape damage, folds, adhesion of foreign matter such as oil or fingerprints thereto, or the like.
Also, in the conventional magnetic tape cassette constructed as described above, when the front lid is operated or pivotally moved to uncover the front opening of the casing, the rear lid is moved away from the magnetic tape, as it is associated with the movement of the front lid. In the operation of covering the front opening, the front lid and rear lid are brought together to envelope and protect the magnetic tape therebetween.
In the conventional tape cassette constructed in such a manner that, as shown in FIG. 1. the front lid 100 and rear lid 102 abut against each other at the association region 104 therebetween. A similar construction is shown in U.S. Pat. No. 4,418,373, FIGS. 4-6.
More particularly, in such prior art, the front lid is continuously biased by spring means to a closing direction, and eventually the lower end thereof comes in contact with the lower end of the rear lid to close the space for the magnetic tape during nonuse of the cassette.
However, when the tape cassette is inaccurately manufactured or assembled, parts other than the lower ends of the front and rear lids come in contact with each other earlier than the lower ends of the front and rear lids do. For example, in the case of FIG. 2, bottom edges of both side ends of the front lid 26 and upper surfaces of the ports 24, and in the case of U.S. Pat. No. 4,418,373, inclined surface portions 42, 44, 43 and 45 (FIG. 4, Col. 4, lines 18-20) correspond to the above described "other parts".
In such a case, the lower ends of the front and rear lids are left open, resulting in a sealing effect deteriorating and dust being allowed to enter the space for the magnetic tape during nonuse of the cassette.
In other words, in the prior art, the size of the gap between the lower ends of the front and rear lids changes depending on the relative rotating angle of the front and rear lids. The size of this angle depends on the accuracy of the manufacturing and assembling of the front and rear lids or other parts which will come into contact with each other when the front portion of the cassette is covered by the front and rear lids.
Therefore, in order to maintain the sealing effect of the lower ends of the front and rear lids, it has been necessary to manufacture and assemble the conventional tape cassette with high accuracy, thus causing the manufacturing cost of the tape cassette to increase.
Also, in the conventional magnetic tape cassette of the type, shown in U.S. Pat. No. 4,844,377, FIG. 11, and in Japanese Patent Publication No. 63-39995, FIGS. 5 to 8, the front lid is formed with a recess by removing the corner of the lower surface of the inner surface of the front lid and the rear lid is engaged with the front lid through the so-formed recess of the front lid to form a labyrinth path when the opening of the casing is closed by the lids, resulting in a disadvantage being encountered in that the front and rear lids are sometimes difficult to separate from each other by lifting up the front lid when preparing to operate the cassette, as labyrinth parts interfere with each other, due to inaccurate manufacturing or assembling.
In order to avoid such a problem, it is required to provide a certain degree of backlash between the front lid and the rear lid. However, the formation of such a backlash likewise deteriorates the form stability of the casing, resulting in a failure to satisfactorily close the casing. In particular, when the tape cassette is subjected to deformation, this clearance is easily increased by a slight movement of the front lid, resulting in a failure to prevent dust or the like from entering the casing and a deterioration in the form stability.
As described above, the conventional magnetic tape cassette fails to exhibit a dust function, due to the increase in the gap between the lower ends of the front and rear lids, which gap is a result of the relative displacement of the front and the rear lids, even if such a displacement is slight.
Accordingly, it would be highly desirable to develop a magnetic tape cassette which is capable of maintaining the sealing effect of the lower ends of the front and rear lids in good condition, even when the front lid is slightly displaced relative to the rear lid.